I have the expression of one gene for 273 glioma patients, as well as their clinical data. I want to do a survival analysis and generate a Kaplan-Meier plot of the patients' survival based on the expression of the gene: "high" or "low". I saw this tutorial on Biostars (Tutorial: Survival analysis with gene expression), and the author takes the Z-score of the expression data to stratify expression as high or low. However, the Z-score is based on the expression of all genes per patient (i.e. taking the average expression and standard deviation of all genes for every patient). Since I don't have the expression of other genes, is it appropriate to take the Z-score for the expression of this gene across all patients (i.e. use the average expression and standard deviation of this gene for all the patients) and stratify high or low expression based on that? Or does survival analysis with gene expression have to be based on the expression of genes per patient, rather than one gene across all patients? I hope this makes sense, please let me know if I need to clarify more.